This invention relates to a magnetic head for a magnetic recording apparatus (hereinafter referred to simply as the "magnetic head"). More particularly, the present invention relates to a magnetic head consisting of two magnetic blocks of high permeability facing each other via a gap on the portion facing the magnetic recording medium, at least one of the blocks having a magnetic core consisting of single crystal ferrite.
Demands are extremely strong nowadays for higher development of magnetic recording technology, especially for higher density magnetic recording. In order to meet the demands, sharp improvements of the recording characteristics, reproducing sensitivity and reduction of noise along with enhancement of coercive force and magnetic flux density must be accomplished.
Magnetic heads that are commonly employed at present have the construction such as shown in FIG. 1, for example, in which coils 13, 13' are respectively wound on magnetic cores formed by so coupling two magnetic blocks 11 and 11' of high permeability as to define a coil-winding window 10 via a gap 12. Single crystal ferrite is generally known as the magnetic material of high permeability for forming the magnetic core. Cubic system Mn-Zn ferrite is generally employed as the single crystal ferrite. In comparison with metal alloys such as permalloy and senalloy (Fe-Al-Si), this ferrite single crystal is more excellent in high frequency characteristics and wear resistance but is not free from the drawbacks that rubbing noise with respect to a recording medium such as a magnetic tape and modulation noise are great.
To reduce the rubbing noise, various proposals have heretofore been made as exemplified by Japanese Patent Publication Nos. 24998/1977, 24999/1977 and 32691/1978. These prior art proposals are characterized by use of Mn-Zn ferrite single core as the magnetic core, Mn-Zn ferrite single core having separated different substances such as SnO.sub.2 by heat-treatment. This SnO.sub.2 different substance is non-magnetic and is generally from 0.1 to several .mu.m in width and 1 to several scores (.mu.m) in length.
Along with improvements in higher density magnetic recording in recent years, however, the track width t.sub.w, gap length g.sub.l and gap depth g.sub.d of the magnetic head have been reduced markedly. By way of example, in the magnetic head of a video tape recorder for home use such as shown in FIG. 2, t.sub.w, g.sub.l and g.sub.d are only about 30 .mu.m, 0.5 .mu.m and 50 .mu.m, respectively and as to the gap length especially, accuracy of about .+-.0.05 .mu.m is required. In the drawing, reference numeral 20 represents the coil-winding window, 21 and 21' represent the ferrite blocks and 22 represents the gap. Reference numerals 23 and 23' represent the coils, 24 designates the filling glass and 25 and 25' represent the portions facing the magnetic recording medium. Reference numeral 26 represent the gap-forming plane. If the abovementioned ferrite material in which considerably great non-magnetic materials are separated is employed as the head material, effective g.sub.l increases whereas effective g.sub.d and t.sub.w decrease because the different materials are magnetically equivalent to the gap, thus causing deterioration and variation of the recording and reproducing characteristics and fluctuation of the characteristics due to wear. As compared with the material in which different substances are separated, the material in which the different substances are separated is inferior in the wear resistance and has greater coercive force. These problems hold true for the magnetic heads for magnetic audio apparatus.
For the abovementioned reasons, a low noise material devoid of the different substances, that are magnetically equivalent to the gap, is preferred as the magnetic material for the magnetic head. As to the noise of the ferrite head, however, the modulation noise accounts for the major proportion and hence, for the purpose of noise reduction, it is more preferred to reduce the modulation noise.
In order to obtain a magnetic head having higher performances, it is therefore necessary to look for a magnetic substance of high permeability in which no different substance exists.
If such single crystalline magnetic materials having a reduced modulation noise are obtained, a magnetic head having the highest write-and-read characteristics and the most excellent carrier signal-to-noise ratio is then prepared. The Mn-Zn ferrite generally exhibits the magnetic anisotropy having the easy axis of magnetization in the direction of &lt;100&gt; or &lt;111&gt; in accordance with the proportions of Fe.sub.2 O.sub.3, MnO and ZnO as its principal components.
However, the disposition of the crystalline axes inside the magnetic core of the magnetic head has not sufficiently been examined and no definite guiding principle has yet been established.
It is quite natural that the write-and-read characteristics of the magnetic head depends upon the mode of distribution of magnetic reluctances inside the magnetic core.
However, it is difficult to obtain detailed information of the surface work of the ferrite, especially of changes in the magnetic characteristics due to work in the proximity of the gap which strongly determines the characteristics of the magnetic head. Namely, it is extremely difficult to estimate what distribution of magnetic reluctances is accomplished how the crystalline orientation is disposed under what work conditions. Even if such estimation is possible, it is extremely difficult, even by use of a presently available high performance computers, to calculate how the axes of magnetic anisotropy be disposed at the gap in order to obtain the best write-and-read characteristics. This may be the primary reason why the desirable disposition of the crystalline axes in the magnetic core is extremely indefinite.
The following references are cited to show the state of the art:
______________________________________ (1) Japanese Patent Publication No. 24998/1977 (2) Japanese Patent Publication No. 24999/1977 (3) Japanese Patent Publication No. 32691/1978 ______________________________________